The present invention relates to a new and improved method of, and apparatus for, regulating the ink viscosity in an ink jet printing system.
In its more particular aspects, the present invention specifically relates to a new and improved method of, and apparatus for, regulating the ink viscosity in an ink jet printing system containing at least one ink jet printing or spraying head. Ink droplets are formed in the ink jet printing or spraying head which are electrically charged and deflected during an ink jet printing operation. Printing ink is supplied to the ink jet printing head from associated medium reservoirs and through an operatively connected line or conduit system.
In known ink jet printing systems the dynamic viscosity or internal friction of the ink is an essential factor affecting the operating reliability of the ink jet printing system. Due to the necessary continuous suction applied at the drop catcher or ink droplet catch gutter by means of a suction pump, there is also sucked in a considerable amount of air from the environment. In addition, an overpressure builds up in the main ink reservoir which requires deaeration which, in turn, influences the ink viscosity. Simultaneously with such deaeration of the main ink reservoir or tank, solvent vapors pass into the environment which, in turn, leads to a change in the ink viscosity. As soon as the permitted viscosity range of the ink is exceeded, i.e. the ink becomes more viscous, satisfactory ink drop formation as well as the charging and deflection of the ink drops and consequently a satisfactory printing function are no longer ensured.